This part was developed by Bosch to solve the fuel pump hum problem
The fuel pressure relief valve is located on the high pressure injection pump (front of the engine) This has a tall hex head, which points straight down. This part may be removed and replaced without removing the pump.
This part fixes the annoying hum associated with (mostly) 2004 Sprinters. There is a loud hum when the vehicle reaches operating temperature, which can be cured by replacing the fuel pressure relief valve on the high pressure pump (located on front of engine). It is somewhat difficult to access the FPRV and may require removal of the serpentine belt. Once replaced - no more annoying hum!